Are higher numbers (2800, 3000, 3200, 3600) factory stock or factory overclocked?
If NOT overclocking, would higher number make the differences verses using 2133 (or 2400 @ 1.35v)?
If installing higher numbers, would it get hotter or same? Or better question, all 1.35v would be same, yet 1.2v is little cooler since it's "lower" voltage? Again, no overclocking.
I am looking at 2x8GB, since it's in lower $100 (vs. 2x16GB is $200).
Plan to get 6700K (even I am not plan to overclock). I MIGHT look into other CPUs (non-K, etc). I am trying to see if I should get H170 (then of course non-K CPU) or Z170. Would Z170 run overall "faster" (even not overclocking) or "same" next to H170 with same CPU, RAM, etc.
Years ago, we used to talk about "FSB", but not nowadays? Same for RAM timings, it doesn't matter anymore?
I'm not sure about the higher memory speed ratings, which ones are going to be "stock" settings ala XMP or if you have to do anything more manually since I've never really looked into DDR4
But IMO, based on what I've seen, most of the answer to your questions is likely to be "its negligible" or "doesn't matter". The only case where memory bandwidth really seems to matter to a CPU anymore is if you're using the on-die GPU. If you were going to rely on that, you'd want the fastest memory you could get your hands on, but otherwise it seems pretty much pointless. Heat differences between sticks running at their rated speed is probably in the noise and not worth worrying about.
If it was me, I'd probably get faster than 2133, just because you could get reasonably priced 2133 DDR3, and if I'm getting DDR4 then I want faster just because. I wouldn't pay a lot more for it though, or if you could get more capacity for the same cost, that would probably be the better choice.